The present disclosure relates generally to wireless communication systems, and more particularly, to spreading techniques for frequency-shift keying (FSK) modulation.
Wireless communication systems are widely deployed to provide various telecommunication services such as telephony, video, data, messaging, and broadcasts. Typical wireless communication systems may employ multiple-access technologies capable of supporting communication with multiple users by sharing available system resources (e.g., bandwidth, transmit power). Examples of such multiple-access technologies include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, orthogonal frequency division multiple access (OFDMA) systems, single-carrier frequency divisional multiple access (SC-FDMA) systems, and time division synchronous code division multiple access (TD-SCDMA) systems.
These multiple access technologies have been adopted in various telecommunication standards to provide a common protocol that enables different wireless devices to communicate on a municipal, national, regional, and even global level. An example of a telecommunication standard is Long Term Evolution (LTE). LTE is a set of enhancements to the Universal Mobile Telecommunications System (UMTS) mobile standard promulgated by Third Generation Partnership Project (3GPP). Generally, a wireless multiple-access communication system can simultaneously support communication for multiple wireless terminals (e.g., user equipment (UE)), each of which can communicate with one or more base stations over downlink or uplink resources.
FSK is a conventional frequency modulation scheme used in wireless communication systems. FSK modulation is known to be power-efficient and to reduce interference between wireless devices. Therefore, for a wireless network where wireless devices are battery limited (e.g., internet-of-things, IoT, devices) and need to share the network with many other wireless devices, FSK is a good candidate for those wireless devices to modulate their uplink signals. However, when there are multiple wireless devices transmitting FSK-modulated signals to a base station, it can be difficult for the base station to decode the FSK-modulated signals to a unique signal transmitted by each of the wireless devices. Therefore, it is desirable to have techniques to handle the detection of multiple users (i.e., multi-user detection) in a wireless communications system when FSK modulation is used.